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<a href="thread__lcl__str__appender_8hpp.html">Go to the documentation of this file.</a><div class="fragment"><div class="line"><a id="l00001" name="l00001"></a><span class="lineno">    1</span><span class="comment">/* Flow</span></div>
<div class="line"><a id="l00002" name="l00002"></a><span class="lineno">    2</span><span class="comment"> * Copyright 2023 Akamai Technologies, Inc.</span></div>
<div class="line"><a id="l00003" name="l00003"></a><span class="lineno">    3</span><span class="comment"> *</span></div>
<div class="line"><a id="l00004" name="l00004"></a><span class="lineno">    4</span><span class="comment"> * Licensed under the Apache License, Version 2.0 (the</span></div>
<div class="line"><a id="l00005" name="l00005"></a><span class="lineno">    5</span><span class="comment"> * &quot;License&quot;); you may not use this file except in</span></div>
<div class="line"><a id="l00006" name="l00006"></a><span class="lineno">    6</span><span class="comment"> * compliance with the License.  You may obtain a copy</span></div>
<div class="line"><a id="l00007" name="l00007"></a><span class="lineno">    7</span><span class="comment"> * of the License at</span></div>
<div class="line"><a id="l00008" name="l00008"></a><span class="lineno">    8</span><span class="comment"> *</span></div>
<div class="line"><a id="l00009" name="l00009"></a><span class="lineno">    9</span><span class="comment"> *   https://www.apache.org/licenses/LICENSE-2.0</span></div>
<div class="line"><a id="l00010" name="l00010"></a><span class="lineno">   10</span><span class="comment"> *</span></div>
<div class="line"><a id="l00011" name="l00011"></a><span class="lineno">   11</span><span class="comment"> * Unless required by applicable law or agreed to in</span></div>
<div class="line"><a id="l00012" name="l00012"></a><span class="lineno">   12</span><span class="comment"> * writing, software distributed under the License is</span></div>
<div class="line"><a id="l00013" name="l00013"></a><span class="lineno">   13</span><span class="comment"> * distributed on an &quot;AS IS&quot; BASIS, WITHOUT WARRANTIES OR</span></div>
<div class="line"><a id="l00014" name="l00014"></a><span class="lineno">   14</span><span class="comment"> * CONDITIONS OF ANY KIND, either express or implied.</span></div>
<div class="line"><a id="l00015" name="l00015"></a><span class="lineno">   15</span><span class="comment"> * See the License for the specific language governing</span></div>
<div class="line"><a id="l00016" name="l00016"></a><span class="lineno">   16</span><span class="comment"> * permissions and limitations under the License. */</span></div>
<div class="line"><a id="l00017" name="l00017"></a><span class="lineno">   17</span><span class="comment"></span> </div>
<div class="line"><a id="l00018" name="l00018"></a><span class="lineno">   18</span><span class="comment">/// @file</span></div>
<div class="line"><a id="l00019" name="l00019"></a><span class="lineno">   19</span><span class="comment"></span><span class="preprocessor">#pragma once</span></div>
<div class="line"><a id="l00020" name="l00020"></a><span class="lineno">   20</span> </div>
<div class="line"><a id="l00021" name="l00021"></a><span class="lineno">   21</span><span class="preprocessor">#include &quot;<a class="code" href="detail_2log__fwd_8hpp.html">flow/log/detail/log_fwd.hpp</a>&quot;</span></div>
<div class="line"><a id="l00022" name="l00022"></a><span class="lineno">   22</span><span class="preprocessor">#include &quot;<a class="code" href="string__ostream_8hpp.html">flow/util/string_ostream.hpp</a>&quot;</span></div>
<div class="line"><a id="l00023" name="l00023"></a><span class="lineno">   23</span><span class="preprocessor">#include &quot;<a class="code" href="uniq__id__holder_8hpp.html">flow/util/uniq_id_holder.hpp</a>&quot;</span></div>
<div class="line"><a id="l00024" name="l00024"></a><span class="lineno">   24</span><span class="preprocessor">#include &lt;boost/iostreams/device/array.hpp&gt;</span></div>
<div class="line"><a id="l00025" name="l00025"></a><span class="lineno">   25</span><span class="preprocessor">#include &lt;boost/iostreams/stream.hpp&gt;</span></div>
<div class="line"><a id="l00026" name="l00026"></a><span class="lineno">   26</span><span class="preprocessor">#include &lt;boost/iostreams/stream_buffer.hpp&gt;</span></div>
<div class="line"><a id="l00027" name="l00027"></a><span class="lineno">   27</span><span class="preprocessor">#include &lt;boost/io/ios_state.hpp&gt;</span></div>
<div class="line"><a id="l00028" name="l00028"></a><span class="lineno">   28</span><span class="preprocessor">#include &lt;boost/move/unique_ptr.hpp&gt;</span></div>
<div class="line"><a id="l00029" name="l00029"></a><span class="lineno">   29</span><span class="preprocessor">#include &lt;boost/unordered_map.hpp&gt;</span></div>
<div class="line"><a id="l00030" name="l00030"></a><span class="lineno">   30</span><span class="preprocessor">#include &lt;boost/thread.hpp&gt;</span></div>
<div class="line"><a id="l00031" name="l00031"></a><span class="lineno">   31</span><span class="preprocessor">#include &lt;string&gt;</span></div>
<div class="line"><a id="l00032" name="l00032"></a><span class="lineno">   32</span> </div>
<div class="line"><a id="l00033" name="l00033"></a><span class="lineno">   33</span><span class="keyword">namespace </span><a class="code hl_namespace" href="namespaceflow_1_1log.html">flow::log</a></div>
<div class="line"><a id="l00034" name="l00034"></a><span class="lineno">   34</span>{</div>
<div class="line"><a id="l00035" name="l00035"></a><span class="lineno">   35</span><span class="comment"></span> </div>
<div class="line"><a id="l00036" name="l00036"></a><span class="lineno">   36</span><span class="comment">/**</span></div>
<div class="line"><a id="l00037" name="l00037"></a><span class="lineno">   37</span><span class="comment"> * Internal flow::log class that facilitates a more efficient way to get util::ostream_op_to_string() behavior</span></div>
<div class="line"><a id="l00038" name="l00038"></a><span class="lineno">   38</span><span class="comment"> * by allowing each thread to repeatedly reuse the structures that function creates from scratch on stack each time it</span></div>
<div class="line"><a id="l00039" name="l00039"></a><span class="lineno">   39</span><span class="comment"> * is invoked; furthermore each logging entity is allotted a separate such set of structures to enable each entity to</span></div>
<div class="line"><a id="l00040" name="l00040"></a><span class="lineno">   40</span><span class="comment"> * not affect the streams of other entities.</span></div>
<div class="line"><a id="l00041" name="l00041"></a><span class="lineno">   41</span><span class="comment"> *</span></div>
<div class="line"><a id="l00042" name="l00042"></a><span class="lineno">   42</span><span class="comment"> * The problem statement arises from util::ostream_op_to_string()&#39;s only obvious flaw which is performance.</span></div>
<div class="line"><a id="l00043" name="l00043"></a><span class="lineno">   43</span><span class="comment"> * One invokes that function and passes a target `std::string` and a sequence of `ostream`-writing operations.  Usually</span></div>
<div class="line"><a id="l00044" name="l00044"></a><span class="lineno">   44</span><span class="comment"> * the `string` has just been newly created `{` locally `}`; and the function itself will ultimately create some Boost</span></div>
<div class="line"><a id="l00045" name="l00045"></a><span class="lineno">   45</span><span class="comment"> * `iostreams` machinery `{` locally `}` and then use it to efficiently write through that machinery into the `string`.</span></div>
<div class="line"><a id="l00046" name="l00046"></a><span class="lineno">   46</span><span class="comment"> * That&#39;s all fine, but if the function is very often invoked, it would be nice</span></div>
<div class="line"><a id="l00047" name="l00047"></a><span class="lineno">   47</span><span class="comment"> * to instead reuse a global `string` *and* associated machinery between invocations.  (`ostream_op_to_string()` can</span></div>
<div class="line"><a id="l00048" name="l00048"></a><span class="lineno">   48</span><span class="comment"> * reuse an existing `string`, but even then it&#39;ll need to re-create the `iostreams` machinery each time.)</span></div>
<div class="line"><a id="l00049" name="l00049"></a><span class="lineno">   49</span><span class="comment"> * In particular, logging machinery (`FLOW_LOG_*()` especially) indeed very often invokes such behavior and could thus</span></div>
<div class="line"><a id="l00050" name="l00050"></a><span class="lineno">   50</span><span class="comment"> * benefit (hence the inspiration behind this class).</span></div>
<div class="line"><a id="l00051" name="l00051"></a><span class="lineno">   51</span><span class="comment"> *</span></div>
<div class="line"><a id="l00052" name="l00052"></a><span class="lineno">   52</span><span class="comment"> * Well, using global structures is not OK: multiple threads will corrupt any such structures by writing and/or</span></div>
<div class="line"><a id="l00053" name="l00053"></a><span class="lineno">   53</span><span class="comment"> * reading concurrently to/from them.  However, if one creates a structure per thread -- a/k/a a thread-local</span></div>
<div class="line"><a id="l00054" name="l00054"></a><span class="lineno">   54</span><span class="comment"> * structure -- then that danger goes away completely.  That is the principle behind this class.  Firstly, from the</span></div>
<div class="line"><a id="l00055" name="l00055"></a><span class="lineno">   55</span><span class="comment"> * class user&#39;s perspective, the class itself is a singleton per thread.  Call get_this_thread_string_appender() to</span></div>
<div class="line"><a id="l00056" name="l00056"></a><span class="lineno">   56</span><span class="comment"> * access the current thread&#39;s only instance of Thread_local_string_appender.  Now you have a pointer to that</span></div>
<div class="line"><a id="l00057" name="l00057"></a><span class="lineno">   57</span><span class="comment"> * object.  Further use is very simple: fresh_appender_ostream() clears the internally stored target string and</span></div>
<div class="line"><a id="l00058" name="l00058"></a><span class="lineno">   58</span><span class="comment"> * returns a pointer to an `ostream` object.  Write to this `ostream` like any other `ostream`.  Once done doing so,</span></div>
<div class="line"><a id="l00059" name="l00059"></a><span class="lineno">   59</span><span class="comment"> * call target_contents(), which will return a reference to the read-only string which has been appended to with</span></div>
<div class="line"><a id="l00060" name="l00060"></a><span class="lineno">   60</span><span class="comment"> * the aforementioned `ostream` writing.  Repeat each time you&#39;d like to write to a string, and then quickly access</span></div>
<div class="line"><a id="l00061" name="l00061"></a><span class="lineno">   61</span><span class="comment"> * that string.</span></div>
<div class="line"><a id="l00062" name="l00062"></a><span class="lineno">   62</span><span class="comment"> *</span></div>
<div class="line"><a id="l00063" name="l00063"></a><span class="lineno">   63</span><span class="comment"> * Update: A further level of indirection/lookup was added when I realized that, for each thread, it&#39;s not desirable</span></div>
<div class="line"><a id="l00064" name="l00064"></a><span class="lineno">   64</span><span class="comment"> * that logically separate stream writers (typically each allotted its own writing object, e.g., a Logger) all write</span></div>
<div class="line"><a id="l00065" name="l00065"></a><span class="lineno">   65</span><span class="comment"> * to one common stream.  Even if their writes are not interleaved within an &quot;atomic&quot; sequence of characters,</span></div>
<div class="line"><a id="l00066" name="l00066"></a><span class="lineno">   66</span><span class="comment"> * state-changing `ostream` formatters (`std::hex` and the like) would cause one writer to affect the formatting of</span></div>
<div class="line"><a id="l00067" name="l00067"></a><span class="lineno">   67</span><span class="comment"> * another, which is not desired (though maybe not immediately obvious due to formatting being a relatively rarely</span></div>
<div class="line"><a id="l00068" name="l00068"></a><span class="lineno">   68</span><span class="comment"> * used feature for many).  Therefore, each writing &quot;entity&quot; is allotted a separate instance of this class, and</span></div>
<div class="line"><a id="l00069" name="l00069"></a><span class="lineno">   69</span><span class="comment"> * lookup is (implicitly) via thread ID and (explicitly) via a source object ID which uniquely (over all time)</span></div>
<div class="line"><a id="l00070" name="l00070"></a><span class="lineno">   70</span><span class="comment"> * identifies each object.</span></div>
<div class="line"><a id="l00071" name="l00071"></a><span class="lineno">   71</span><span class="comment"> *</span></div>
<div class="line"><a id="l00072" name="l00072"></a><span class="lineno">   72</span><span class="comment"> *   ~~~</span></div>
<div class="line"><a id="l00073" name="l00073"></a><span class="lineno">   73</span><span class="comment"> *   // If you frequently do this, from one or from multiple threads:</span></div>
<div class="line"><a id="l00074" name="l00074"></a><span class="lineno">   74</span><span class="comment"> *   class Distinct_writer</span></div>
<div class="line"><a id="l00075" name="l00075"></a><span class="lineno">   75</span><span class="comment"> *   {</span></div>
<div class="line"><a id="l00076" name="l00076"></a><span class="lineno">   76</span><span class="comment"> *     ...</span></div>
<div class="line"><a id="l00077" name="l00077"></a><span class="lineno">   77</span><span class="comment"> *       string output;</span></div>
<div class="line"><a id="l00078" name="l00078"></a><span class="lineno">   78</span><span class="comment"> *       // Expensive structure setup occurs before the stream writing can execute.  (Terminating `flush` is assumed.)</span></div>
<div class="line"><a id="l00079" name="l00079"></a><span class="lineno">   79</span><span class="comment"> *       util::ostream_op_to_string(&amp;output, &quot;The answer is: [&quot;, std::hex, 42, &quot;].&quot;);</span></div>
<div class="line"><a id="l00080" name="l00080"></a><span class="lineno">   80</span><span class="comment"> *       log_string(output); // Suppose log_string() takes const std::string&amp;.</span></div>
<div class="line"><a id="l00081" name="l00081"></a><span class="lineno">   81</span><span class="comment"> *       log_chars(output.c_str()); // Or suppose log_chars() takes const char*.</span></div>
<div class="line"><a id="l00082" name="l00082"></a><span class="lineno">   82</span><span class="comment"> *       // std::hex formatting is forgotten, as each util::ostream_op_to_string() creates a new everything.</span></div>
<div class="line"><a id="l00083" name="l00083"></a><span class="lineno">   83</span><span class="comment"> *     ...</span></div>
<div class="line"><a id="l00084" name="l00084"></a><span class="lineno">   84</span><span class="comment"> *   }</span></div>
<div class="line"><a id="l00085" name="l00085"></a><span class="lineno">   85</span><span class="comment"> *</span></div>
<div class="line"><a id="l00086" name="l00086"></a><span class="lineno">   86</span><span class="comment"> *   // Then consider replacing it with this (for better performance over time):</span></div>
<div class="line"><a id="l00087" name="l00087"></a><span class="lineno">   87</span><span class="comment"> *   class Distinct_writer : private util::Unique_id_holder</span></div>
<div class="line"><a id="l00088" name="l00088"></a><span class="lineno">   88</span><span class="comment"> *   {</span></div>
<div class="line"><a id="l00089" name="l00089"></a><span class="lineno">   89</span><span class="comment"> *     ...</span></div>
<div class="line"><a id="l00090" name="l00090"></a><span class="lineno">   90</span><span class="comment"> *       // Note lookup by `this`: we are also a Unique_id_holder which means this can get our unique ID.</span></div>
<div class="line"><a id="l00091" name="l00091"></a><span class="lineno">   91</span><span class="comment"> *       auto const appender = log::Thread_local_string_appender::get_this_thread_string_appender(*this);</span></div>
<div class="line"><a id="l00092" name="l00092"></a><span class="lineno">   92</span><span class="comment"> *       // Note added explicit `flush`.</span></div>
<div class="line"><a id="l00093" name="l00093"></a><span class="lineno">   93</span><span class="comment"> *       *(appender-&gt;fresh_appender_ostream()) &lt;&lt; &quot;The answer is: [&quot; &lt;&lt; std::hex &lt;&lt; 42 &lt;&lt; &quot;].&quot; &lt;&lt; std::flush;</span></div>
<div class="line"><a id="l00094" name="l00094"></a><span class="lineno">   94</span><span class="comment"> *       log_string(appender-&gt;target_contents());</span></div>
<div class="line"><a id="l00095" name="l00095"></a><span class="lineno">   95</span><span class="comment"> *       log_chars(appender-&gt;target_contents().c_str());</span></div>
<div class="line"><a id="l00096" name="l00096"></a><span class="lineno">   96</span><span class="comment"> *       // Additional feature: std::hex formatting will persist for further such snippets, for the current thread.</span></div>
<div class="line"><a id="l00097" name="l00097"></a><span class="lineno">   97</span><span class="comment"> *     ...</span></div>
<div class="line"><a id="l00098" name="l00098"></a><span class="lineno">   98</span><span class="comment"> *   }</span></div>
<div class="line"><a id="l00099" name="l00099"></a><span class="lineno">   99</span><span class="comment"> *   ~~~</span></div>
<div class="line"><a id="l00100" name="l00100"></a><span class="lineno">  100</span><span class="comment"> *</span></div>
<div class="line"><a id="l00101" name="l00101"></a><span class="lineno">  101</span><span class="comment"> * Note, once again, that because get_this_thread_string_appender() returns a thread-local object, it is by definition</span></div>
<div class="line"><a id="l00102" name="l00102"></a><span class="lineno">  102</span><span class="comment"> * impossible to corrupt anything inside it due to multiple threads writing to it.  (That is unless, of course, you</span></div>
<div class="line"><a id="l00103" name="l00103"></a><span class="lineno">  103</span><span class="comment"> * try passing that pointer to another thread and writing to it there, but that&#39;s basically malicious behavior;</span></div>
<div class="line"><a id="l00104" name="l00104"></a><span class="lineno">  104</span><span class="comment"> * so don&#39;t do that.)</span></div>
<div class="line"><a id="l00105" name="l00105"></a><span class="lineno">  105</span><span class="comment"> *</span></div>
<div class="line"><a id="l00106" name="l00106"></a><span class="lineno">  106</span><span class="comment"> * ### Thread safety ###</span></div>
<div class="line"><a id="l00107" name="l00107"></a><span class="lineno">  107</span><span class="comment"> * Well, see above.  If you use class as prescribed, then it&#39;s safe to read and write without locking around</span></div>
<div class="line"><a id="l00108" name="l00108"></a><span class="lineno">  108</span><span class="comment"> * object of this class.</span></div>
<div class="line"><a id="l00109" name="l00109"></a><span class="lineno">  109</span><span class="comment"> *</span></div>
<div class="line"><a id="l00110" name="l00110"></a><span class="lineno">  110</span><span class="comment"> * ### Memory use ###</span></div>
<div class="line"><a id="l00111" name="l00111"></a><span class="lineno">  111</span><span class="comment"> * The object itself is not large, storing some streams and ancillary stream-related obejcts.</span></div>
<div class="line"><a id="l00112" name="l00112"></a><span class="lineno">  112</span><span class="comment"> * The lookup table just indexes by object ID and thread ID, so a few integers per writing entity per writing thread.</span></div>
<div class="line"><a id="l00113" name="l00113"></a><span class="lineno">  113</span><span class="comment"> * The implementation we use ensures that once a given thread disappears, all the data for that thread ID are freed.</span></div>
<div class="line"><a id="l00114" name="l00114"></a><span class="lineno">  114</span><span class="comment"> * Let us then discuss, from this point forth, what happens while a given thread is alive.  Namely:</span></div>
<div class="line"><a id="l00115" name="l00115"></a><span class="lineno">  115</span><span class="comment"> *</span></div>
<div class="line"><a id="l00116" name="l00116"></a><span class="lineno">  116</span><span class="comment"> * There is no way to remove an appender from this table once it has been added which can be seen as a</span></div>
<div class="line"><a id="l00117" name="l00117"></a><span class="lineno">  117</span><span class="comment"> * memory leak.  In practice, the original use case of Logger means the number of lookup table entries is not likely</span></div>
<div class="line"><a id="l00118" name="l00118"></a><span class="lineno">  118</span><span class="comment"> * to grow large enough to matter -- but extreme scenarios contradicting this estimation may be contrived or occur.</span></div>
<div class="line"><a id="l00119" name="l00119"></a><span class="lineno">  119</span><span class="comment"> *</span></div>
<div class="line"><a id="l00120" name="l00120"></a><span class="lineno">  120</span><span class="comment"> * In terms of implementation, getting cleanup to work is extremely difficult and possibly essentially impossible.</span></div>
<div class="line"><a id="l00121" name="l00121"></a><span class="lineno">  121</span><span class="comment"> * (This is true because it&#39;s not possible, without some kind of undocumented and possibly un-portable hackery, to</span></div>
<div class="line"><a id="l00122" name="l00122"></a><span class="lineno">  122</span><span class="comment"> * enumerate all the threads from which a given object has created a Thread_local_string_appender.  Even if one could,</span></div>
<div class="line"><a id="l00123" name="l00123"></a><span class="lineno">  123</span><span class="comment"> * it is similarly not really possible to do anything about it without entering each such thread, which is quite hard</span></div>
<div class="line"><a id="l00124" name="l00124"></a><span class="lineno">  124</span><span class="comment"> * to do elegantly and unintrusively w/r/t to calling code.  Even if one could enter each such thread, some</span></div>
<div class="line"><a id="l00125" name="l00125"></a><span class="lineno">  125</span><span class="comment"> * kind of locking would probably need to be added, eliminating the elegance of the basic premise of the class which</span></div>
<div class="line"><a id="l00126" name="l00126"></a><span class="lineno">  126</span><span class="comment"> * is that of a thread-local singleton per source object.)  For this reason, adding cleanup is not even listed as a</span></div>
<div class="line"><a id="l00127" name="l00127"></a><span class="lineno">  127</span><span class="comment"> * to-do.</span></div>
<div class="line"><a id="l00128" name="l00128"></a><span class="lineno">  128</span><span class="comment"> *</span></div>
<div class="line"><a id="l00129" name="l00129"></a><span class="lineno">  129</span><span class="comment"> * Since util::Unique_id_holder is unique over all time, not just at any given time, there is no danger that the reuse</span></div>
<div class="line"><a id="l00130" name="l00130"></a><span class="lineno">  130</span><span class="comment"> * of some dead object&#39;s ID will cause a collision.  Historically this was a problem when we used `this` pointers</span></div>
<div class="line"><a id="l00131" name="l00131"></a><span class="lineno">  131</span><span class="comment"> * as IDs (as once an object is gone, its `this` value can be reused by another, new object).</span></div>
<div class="line"><a id="l00132" name="l00132"></a><span class="lineno">  132</span><span class="comment"> *</span></div>
<div class="line"><a id="l00133" name="l00133"></a><span class="lineno">  133</span><span class="comment"> * ### Implementation notes ###</span></div>
<div class="line"><a id="l00134" name="l00134"></a><span class="lineno">  134</span><span class="comment"> * We use boost.thread&#39;s `thread_specific_ptr` to implement a lazily initialized per-thread singleton (in which</span></div>
<div class="line"><a id="l00135" name="l00135"></a><span class="lineno">  135</span><span class="comment"> * a per-object-ID sub-table of Thread_local_string_appender objects lies).  An alternative implementation would</span></div>
<div class="line"><a id="l00136" name="l00136"></a><span class="lineno">  136</span><span class="comment"> * be C++11&#39;s built-in `thread_local` keyword, probably with a `unique_ptr` to wrap each sub-table (to allow for</span></div>
<div class="line"><a id="l00137" name="l00137"></a><span class="lineno">  137</span><span class="comment"> * lazy initialization instead of thread-startup initialization).  The main reason I chose to keep `thread_specific_ptr`</span></div>
<div class="line"><a id="l00138" name="l00138"></a><span class="lineno">  138</span><span class="comment"> * even upon moving from C++03 to C++1x is that we use `boost::thread` -- not `std::thread`.  Experiments show</span></div>
<div class="line"><a id="l00139" name="l00139"></a><span class="lineno">  139</span><span class="comment"> * `thread_local` behaves appropriately (crucially, including cleanup on thread exit) even with</span></div>
<div class="line"><a id="l00140" name="l00140"></a><span class="lineno">  140</span><span class="comment"> * `boost::thread`, but I don&#39;t see this documented anywhere (which doesn&#39;t mean it isn&#39;t documented), and without</span></div>
<div class="line"><a id="l00141" name="l00141"></a><span class="lineno">  141</span><span class="comment"> * that it could be an implementation coincidence as opposed to a formal guarantee.  A secondary reason -- which can</span></div>
<div class="line"><a id="l00142" name="l00142"></a><span class="lineno">  142</span><span class="comment"> * be thought of the straw that broke the camel&#39;s back in this case, as it is fairly minor -- is that</span></div>
<div class="line"><a id="l00143" name="l00143"></a><span class="lineno">  143</span><span class="comment"> * `thread_specific_ptr` provides lazy initialization by default, without needing a `unique_ptr` wrapper;</span></div>
<div class="line"><a id="l00144" name="l00144"></a><span class="lineno">  144</span><span class="comment"> * a given thread&#39;s `p.get()` returns null the first time it is invoked; and executes `delete p.get();` at thread exit</span></div>
<div class="line"><a id="l00145" name="l00145"></a><span class="lineno">  145</span><span class="comment"> * (one need not supply a deleter function, although one could if more complex cleanup were needed).  This is</span></div>
<div class="line"><a id="l00146" name="l00146"></a><span class="lineno">  146</span><span class="comment"> * what a default-constructed `unique_ptr` would give us, but we get it for &quot;free&quot; (in the sense that no added code</span></div>
<div class="line"><a id="l00147" name="l00147"></a><span class="lineno">  147</span><span class="comment"> * is necessary to achieve the same behavior) with `thread_specific_ptr`.</span></div>
<div class="line"><a id="l00148" name="l00148"></a><span class="lineno">  148</span><span class="comment"> */</span></div>
<div class="line"><a id="l00149" name="l00149"></a><span class="lineno"><a class="line" href="classflow_1_1log_1_1Thread__local__string__appender.html">  149</a></span><span class="keyword">class </span><a class="code hl_class" href="classflow_1_1log_1_1Thread__local__string__appender.html">Thread_local_string_appender</a> :</div>
<div class="line"><a id="l00150" name="l00150"></a><span class="lineno">  150</span>  <span class="keyword">private</span> boost::noncopyable</div>
<div class="line"><a id="l00151" name="l00151"></a><span class="lineno">  151</span>{</div>
<div class="line"><a id="l00152" name="l00152"></a><span class="lineno">  152</span><span class="keyword">public</span>:</div>
<div class="line"><a id="l00153" name="l00153"></a><span class="lineno">  153</span>  <span class="comment">// Methods.</span></div>
<div class="line"><a id="l00154" name="l00154"></a><span class="lineno">  154</span><span class="comment"></span> </div>
<div class="line"><a id="l00155" name="l00155"></a><span class="lineno">  155</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00156" name="l00156"></a><span class="lineno">  156</span><span class="comment">   * Returns a pointer to the exactly one Thread_local_string_appender object that is accessible from</span></div>
<div class="line"><a id="l00157" name="l00157"></a><span class="lineno">  157</span><span class="comment">   * the current thread for the given source object.  The source object is given by its ID.  The source object</span></div>
<div class="line"><a id="l00158" name="l00158"></a><span class="lineno">  158</span><span class="comment">   * can store or contain (or be otherwise mapped to) its own util::Unique_id_holder; and thus it can be</span></div>
<div class="line"><a id="l00159" name="l00159"></a><span class="lineno">  159</span><span class="comment">   * any object (e.g., a Logger, in original use case) that desires the use of one distinct (from other</span></div>
<div class="line"><a id="l00160" name="l00160"></a><span class="lineno">  160</span><span class="comment">   * objects) but continuous (meaning any stream state including characters output will persist over time)</span></div>
<div class="line"><a id="l00161" name="l00161"></a><span class="lineno">  161</span><span class="comment">   * `ostream`.  (The `ostream` is not returned directly but rather as the wrapping Thread_local_string_appender</span></div>
<div class="line"><a id="l00162" name="l00162"></a><span class="lineno">  162</span><span class="comment">   * object for that stream.)  Ultimately there is exactly one `ostream` (and Thread_local_string_appender) per</span></div>
<div class="line"><a id="l00163" name="l00163"></a><span class="lineno">  163</span><span class="comment">   * (invoking thread T, `source_obj_id`) pair that has invoked the present method so far, including the current</span></div>
<div class="line"><a id="l00164" name="l00164"></a><span class="lineno">  164</span><span class="comment">   * invocation itself.</span></div>
<div class="line"><a id="l00165" name="l00165"></a><span class="lineno">  165</span><span class="comment">   *</span></div>
<div class="line"><a id="l00166" name="l00166"></a><span class="lineno">  166</span><span class="comment">   * @param source_obj_id</span></div>
<div class="line"><a id="l00167" name="l00167"></a><span class="lineno">  167</span><span class="comment">   *        An ID attached in a 1-to-1 (over all time until program exit) fashion to the entity (typically, class</span></div>
<div class="line"><a id="l00168" name="l00168"></a><span class="lineno">  168</span><span class="comment">   *        instance of any type, e.g., Logger) desiring its own Thread_local_string_appender.</span></div>
<div class="line"><a id="l00169" name="l00169"></a><span class="lineno">  169</span><span class="comment">   * @return See above.</span></div>
<div class="line"><a id="l00170" name="l00170"></a><span class="lineno">  170</span><span class="comment">   */</span></div>
<div class="line"><a id="l00171" name="l00171"></a><span class="lineno">  171</span>  <span class="keyword">static</span> <a class="code hl_class" href="classflow_1_1log_1_1Thread__local__string__appender.html">Thread_local_string_appender</a>* <a class="code hl_function" href="classflow_1_1log_1_1Thread__local__string__appender.html#a4c67bd1c2f1ccc58288df86abda02d88">get_this_thread_string_appender</a>(<span class="keyword">const</span> <a class="code hl_class" href="classflow_1_1util_1_1Unique__id__holder.html">util::Unique_id_holder</a>&amp; source_obj_id);</div>
<div class="line"><a id="l00172" name="l00172"></a><span class="lineno">  172</span><span class="comment"></span> </div>
<div class="line"><a id="l00173" name="l00173"></a><span class="lineno">  173</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00174" name="l00174"></a><span class="lineno">  174</span><span class="comment">   * Clears the internally stored string (accessible for reading via target_contents()), and returns an</span></div>
<div class="line"><a id="l00175" name="l00175"></a><span class="lineno">  175</span><span class="comment">   * output stream writing to which will append to that string.  You must `flush` (or flush any other way like</span></div>
<div class="line"><a id="l00176" name="l00176"></a><span class="lineno">  176</span><span class="comment">   * `endl`) the stream in order to ensure characters are actually written to the string.  (I am fairly sure flushing</span></div>
<div class="line"><a id="l00177" name="l00177"></a><span class="lineno">  177</span><span class="comment">   * is in fact THE thing that actually writes to the string.)</span></div>
<div class="line"><a id="l00178" name="l00178"></a><span class="lineno">  178</span><span class="comment">   *</span></div>
<div class="line"><a id="l00179" name="l00179"></a><span class="lineno">  179</span><span class="comment">   * The pointer&#39;s value never changes for `*this` object.  This fact is critical when it comes to the logic</span></div>
<div class="line"><a id="l00180" name="l00180"></a><span class="lineno">  180</span><span class="comment">   * of sequential save_formatting_state_and_restore_prev() calls, as well as (for example) the `ostream` continuity</span></div>
<div class="line"><a id="l00181" name="l00181"></a><span class="lineno">  181</span><span class="comment">   * semantics described in class Logger header (that class uses the present class).</span></div>
<div class="line"><a id="l00182" name="l00182"></a><span class="lineno">  182</span><span class="comment">   *</span></div>
<div class="line"><a id="l00183" name="l00183"></a><span class="lineno">  183</span><span class="comment">   * Behavior is undefined if, at the time the present method is called, the last `flush` of</span></div>
<div class="line"><a id="l00184" name="l00184"></a><span class="lineno">  184</span><span class="comment">   * `*fresh_appender_ostream()` precedes the last writing of actual data to same.  In other words,</span></div>
<div class="line"><a id="l00185" name="l00185"></a><span class="lineno">  185</span><span class="comment">   * always `flush` the stream immediately after writing to it, or else who knows what will happen</span></div>
<div class="line"><a id="l00186" name="l00186"></a><span class="lineno">  186</span><span class="comment">   * with any un-flushed data when one subsequently calls fresh_appender_ostream(), clearing the string?</span></div>
<div class="line"><a id="l00187" name="l00187"></a><span class="lineno">  187</span><span class="comment">   *</span></div>
<div class="line"><a id="l00188" name="l00188"></a><span class="lineno">  188</span><span class="comment">   * Behavior is undefined if you call this from any thread other than the one in which</span></div>
<div class="line"><a id="l00189" name="l00189"></a><span class="lineno">  189</span><span class="comment">   * get_this_thread_string_appender() was called in order to obtain `this`.</span></div>
<div class="line"><a id="l00190" name="l00190"></a><span class="lineno">  190</span><span class="comment">   *</span></div>
<div class="line"><a id="l00191" name="l00191"></a><span class="lineno">  191</span><span class="comment">   * @see save_formatting_state_and_restore_prev() is a valuable technique to enable usability in</span></div>
<div class="line"><a id="l00192" name="l00192"></a><span class="lineno">  192</span><span class="comment">   *      user-facing APIs that use Thread_local_string_appender within the implementation (notably logging</span></div>
<div class="line"><a id="l00193" name="l00193"></a><span class="lineno">  193</span><span class="comment">   *      APIs).  See its doc header before using this method.</span></div>
<div class="line"><a id="l00194" name="l00194"></a><span class="lineno">  194</span><span class="comment">   *</span></div>
<div class="line"><a id="l00195" name="l00195"></a><span class="lineno">  195</span><span class="comment">   * @return Pointer to `ostream` writing to which (followed by flushing) will append to string that</span></div>
<div class="line"><a id="l00196" name="l00196"></a><span class="lineno">  196</span><span class="comment">   *         is accessible via target_contents().</span></div>
<div class="line"><a id="l00197" name="l00197"></a><span class="lineno">  197</span><span class="comment">   */</span></div>
<div class="line"><a id="l00198" name="l00198"></a><span class="lineno">  198</span>  std::ostream* <a class="code hl_function" href="classflow_1_1log_1_1Thread__local__string__appender.html#af8808ca3accc5384a627bb806de4e4b1">fresh_appender_ostream</a>();</div>
<div class="line"><a id="l00199" name="l00199"></a><span class="lineno">  199</span><span class="comment"></span> </div>
<div class="line"><a id="l00200" name="l00200"></a><span class="lineno">  200</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00201" name="l00201"></a><span class="lineno">  201</span><span class="comment">   * Same as fresh_appender_ostream() but does not clear the result string, enabling piecemeal writing to</span></div>
<div class="line"><a id="l00202" name="l00202"></a><span class="lineno">  202</span><span class="comment">   * that string between clearings of the latter.</span></div>
<div class="line"><a id="l00203" name="l00203"></a><span class="lineno">  203</span><span class="comment">   *</span></div>
<div class="line"><a id="l00204" name="l00204"></a><span class="lineno">  204</span><span class="comment">   * @return Identical to fresh_appender_ostream()&#39;s return value.</span></div>
<div class="line"><a id="l00205" name="l00205"></a><span class="lineno">  205</span><span class="comment">   */</span></div>
<div class="line"><a id="l00206" name="l00206"></a><span class="lineno">  206</span>  std::ostream* <a class="code hl_function" href="classflow_1_1log_1_1Thread__local__string__appender.html#a64383811f529af676dde0028f61831f7">appender_ostream</a>();</div>
<div class="line"><a id="l00207" name="l00207"></a><span class="lineno">  207</span><span class="comment"></span> </div>
<div class="line"><a id="l00208" name="l00208"></a><span class="lineno">  208</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00209" name="l00209"></a><span class="lineno">  209</span><span class="comment">   * Saves the formatting state of the `ostream` returned by appender_ostream() and sets that same `ostream`</span></div>
<div class="line"><a id="l00210" name="l00210"></a><span class="lineno">  210</span><span class="comment">   * to the state saved last time this method was called on `*this`, or at its construction, whichever happened</span></div>
<div class="line"><a id="l00211" name="l00211"></a><span class="lineno">  211</span><span class="comment">   * later.  Examples of formatting state are `std::hex` and locale imbuings.</span></div>
<div class="line"><a id="l00212" name="l00212"></a><span class="lineno">  212</span><span class="comment">   *</span></div>
<div class="line"><a id="l00213" name="l00213"></a><span class="lineno">  213</span><span class="comment">   * This is useful if you tend to follow a pattern like the following</span></div>
<div class="line"><a id="l00214" name="l00214"></a><span class="lineno">  214</span><span class="comment">   * macro definition that takes `user_supplied_stream_args` macro argument:</span></div>
<div class="line"><a id="l00215" name="l00215"></a><span class="lineno">  215</span><span class="comment">   *</span></div>
<div class="line"><a id="l00216" name="l00216"></a><span class="lineno">  216</span><span class="comment">   *   ~~~</span></div>
<div class="line"><a id="l00217" name="l00217"></a><span class="lineno">  217</span><span class="comment">   *   *(appender-&gt;fresh_appender_ostream())</span></div>
<div class="line"><a id="l00218" name="l00218"></a><span class="lineno">  218</span><span class="comment">   *     &lt;&lt; __FILE__ &lt;&lt; &#39;:&#39; &lt;&lt; __LINE &lt;&lt; &quot;: &quot; // First standard prefix to identify source of log line...</span></div>
<div class="line"><a id="l00219" name="l00219"></a><span class="lineno">  219</span><span class="comment">   *     &lt;&lt; user_supplied_stream_args         // ...then user-given ostream args (token may expand to multiple &lt;&lt;s)...</span></div>
<div class="line"><a id="l00220" name="l00220"></a><span class="lineno">  220</span><span class="comment">   *     &lt;&lt; &#39;\n&#39;                              // ...then any terminating characters...</span></div>
<div class="line"><a id="l00221" name="l00221"></a><span class="lineno">  221</span><span class="comment">   *     &lt;&lt; std::flush;                       // ...and ensure it&#39;s all flushed into `string target_contents()`.</span></div>
<div class="line"><a id="l00222" name="l00222"></a><span class="lineno">  222</span><span class="comment">   *   ~~~</span></div>
<div class="line"><a id="l00223" name="l00223"></a><span class="lineno">  223</span><span class="comment">   *</span></div>
<div class="line"><a id="l00224" name="l00224"></a><span class="lineno">  224</span><span class="comment">   * If this is done repeatedly, then `user_supplied_stream_args` might include formatting changes like `std::hex`.</span></div>
<div class="line"><a id="l00225" name="l00225"></a><span class="lineno">  225</span><span class="comment">   * In this example, there is the danger that such an `std::hex` from log statement N would then &quot;infect&quot;</span></div>
<div class="line"><a id="l00226" name="l00226"></a><span class="lineno">  226</span><span class="comment">   * the `__LINE__` output from log statement (N + 1), the line # showing up in hex form instead of decimal.</span></div>
<div class="line"><a id="l00227" name="l00227"></a><span class="lineno">  227</span><span class="comment">   * However, if you use the present feature, then the problem will not occur.</span></div>
<div class="line"><a id="l00228" name="l00228"></a><span class="lineno">  228</span><span class="comment">   * However, to avoid similarly surprising the user, restore their formatting with the same call.</span></div>
<div class="line"><a id="l00229" name="l00229"></a><span class="lineno">  229</span><span class="comment">   * The above example would become:</span></div>
<div class="line"><a id="l00230" name="l00230"></a><span class="lineno">  230</span><span class="comment">   *</span></div>
<div class="line"><a id="l00231" name="l00231"></a><span class="lineno">  231</span><span class="comment">   *   ~~~</span></div>
<div class="line"><a id="l00232" name="l00232"></a><span class="lineno">  232</span><span class="comment">   *     auto&amp; os = *appender-&gt;fresh_appender_ostream();</span></div>
<div class="line"><a id="l00233" name="l00233"></a><span class="lineno">  233</span><span class="comment">   *     os.save_formatting_state_and_restore_prev(); // Restore pristine formatting from constuction time.</span></div>
<div class="line"><a id="l00234" name="l00234"></a><span class="lineno">  234</span><span class="comment">   *     os &lt;&lt; __FILE__ &lt;&lt; &#39;:&#39; &lt;&lt; __LINE &lt;&lt; &quot;: &quot;; // Can log prefix without fear of surprising formatting.</span></div>
<div class="line"><a id="l00235" name="l00235"></a><span class="lineno">  235</span><span class="comment">   *     // (Note that if apply formatters here for more exotic output, undo them before the following call.)</span></div>
<div class="line"><a id="l00236" name="l00236"></a><span class="lineno">  236</span><span class="comment">   *     os.save_formatting_state_and_restore_prev(); // Restore formatting from previous user_supplied_stream_args.</span></div>
<div class="line"><a id="l00237" name="l00237"></a><span class="lineno">  237</span><span class="comment">   *     os &lt;&lt; user_supplied_stream_args</span></div>
<div class="line"><a id="l00238" name="l00238"></a><span class="lineno">  238</span><span class="comment">   *        &lt;&lt; &#39;\n&#39; // Formatting probably doesn&#39;t affect this, so no need to worry about restoring state here.</span></div>
<div class="line"><a id="l00239" name="l00239"></a><span class="lineno">  239</span><span class="comment">   *        &lt;&lt; std::flush;</span></div>
<div class="line"><a id="l00240" name="l00240"></a><span class="lineno">  240</span><span class="comment">   *   ~~~</span></div>
<div class="line"><a id="l00241" name="l00241"></a><span class="lineno">  241</span><span class="comment">   *</span></div>
<div class="line"><a id="l00242" name="l00242"></a><span class="lineno">  242</span><span class="comment">   * @note Reminder: All access to a `*this` must occur in one thread by definition.  Therefore there are no</span></div>
<div class="line"><a id="l00243" name="l00243"></a><span class="lineno">  243</span><span class="comment">   *       thread safety concerns to do with the suggested usage patterns.</span></div>
<div class="line"><a id="l00244" name="l00244"></a><span class="lineno">  244</span><span class="comment">   * @note Detail: The formatting features affected are as described in documentation for</span></div>
<div class="line"><a id="l00245" name="l00245"></a><span class="lineno">  245</span><span class="comment">   *       `boost::io::basic_ios_all_saver`.  This can be summarized as everything except user-defined formatters.</span></div>
<div class="line"><a id="l00246" name="l00246"></a><span class="lineno">  246</span><span class="comment">   */</span></div>
<div class="line"><a id="l00247" name="l00247"></a><span class="lineno">  247</span>  <span class="keywordtype">void</span> <a class="code hl_function" href="classflow_1_1log_1_1Thread__local__string__appender.html#a2ac7b443898adf1696d0f24f87481520">save_formatting_state_and_restore_prev</a>();</div>
<div class="line"><a id="l00248" name="l00248"></a><span class="lineno">  248</span><span class="comment"></span> </div>
<div class="line"><a id="l00249" name="l00249"></a><span class="lineno">  249</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00250" name="l00250"></a><span class="lineno">  250</span><span class="comment">   * Read-only accessor for the contents of the `string`, as written to it since the last fresh_appender_ostream()</span></div>
<div class="line"><a id="l00251" name="l00251"></a><span class="lineno">  251</span><span class="comment">   * call, or object construction, whichever occurred later.</span></div>
<div class="line"><a id="l00252" name="l00252"></a><span class="lineno">  252</span><span class="comment">   *</span></div>
<div class="line"><a id="l00253" name="l00253"></a><span class="lineno">  253</span><span class="comment">   * The reference&#39;s value never changes for `*this` object.  The string&#39;s value may change depending on</span></div>
<div class="line"><a id="l00254" name="l00254"></a><span class="lineno">  254</span><span class="comment">   * whether the user writes to `*fresh_appender_ostream()` (which writes to the string) or calls that</span></div>
<div class="line"><a id="l00255" name="l00255"></a><span class="lineno">  255</span><span class="comment">   * method (which clears it).</span></div>
<div class="line"><a id="l00256" name="l00256"></a><span class="lineno">  256</span><span class="comment">   *</span></div>
<div class="line"><a id="l00257" name="l00257"></a><span class="lineno">  257</span><span class="comment">   * Behavior is undefined if you call this from any thread other than the one in which</span></div>
<div class="line"><a id="l00258" name="l00258"></a><span class="lineno">  258</span><span class="comment">   * get_this_thread_string_appender() was called in order to obtain `this`.</span></div>
<div class="line"><a id="l00259" name="l00259"></a><span class="lineno">  259</span><span class="comment">   *</span></div>
<div class="line"><a id="l00260" name="l00260"></a><span class="lineno">  260</span><span class="comment">   * ### Rationale ###</span></div>
<div class="line"><a id="l00261" name="l00261"></a><span class="lineno">  261</span><span class="comment">   * Why return `const string&amp;` instead of util::String_view?  Answer: Same as in doc header of String_ostream::str().</span></div>
<div class="line"><a id="l00262" name="l00262"></a><span class="lineno">  262</span><span class="comment">   *</span></div>
<div class="line"><a id="l00263" name="l00263"></a><span class="lineno">  263</span><span class="comment">   * @return Read-only reference to `string`.</span></div>
<div class="line"><a id="l00264" name="l00264"></a><span class="lineno">  264</span><span class="comment">   */</span></div>
<div class="line"><a id="l00265" name="l00265"></a><span class="lineno">  265</span>  <span class="keyword">const</span> std::string&amp; <a class="code hl_function" href="classflow_1_1log_1_1Thread__local__string__appender.html#a3f1a93d0c468efeafd83fb10e104905f">target_contents</a>() <span class="keyword">const</span>;</div>
<div class="line"><a id="l00266" name="l00266"></a><span class="lineno">  266</span> </div>
<div class="line"><a id="l00267" name="l00267"></a><span class="lineno">  267</span><span class="keyword">private</span>:</div>
<div class="line"><a id="l00268" name="l00268"></a><span class="lineno">  268</span> </div>
<div class="line"><a id="l00269" name="l00269"></a><span class="lineno">  269</span>  <span class="comment">// Types.</span></div>
<div class="line"><a id="l00270" name="l00270"></a><span class="lineno">  270</span><span class="comment"></span> </div>
<div class="line"><a id="l00271" name="l00271"></a><span class="lineno">  271</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00272" name="l00272"></a><span class="lineno">  272</span><span class="comment">   * Short-hand for map of a given thread&#39;s appender objects indexed by the IDs of their respective source objects.</span></div>
<div class="line"><a id="l00273" name="l00273"></a><span class="lineno">  273</span><span class="comment">   * Smart pointers are stored to ensure the Thread_local_string_appender is deleted once removed from such a map.</span></div>
<div class="line"><a id="l00274" name="l00274"></a><span class="lineno">  274</span><span class="comment">   * Thus once a per-thread map disappears at thread exit, all the stored objects within are freed also.</span></div>
<div class="line"><a id="l00275" name="l00275"></a><span class="lineno">  275</span><span class="comment">   */</span></div>
<div class="line"><a id="l00276" name="l00276"></a><span class="lineno"><a class="line" href="classflow_1_1log_1_1Thread__local__string__appender.html#a4656e713b9ac1c6cdad3adde18de70ec">  276</a></span>  <span class="keyword">using </span><a class="code hl_typedef" href="classflow_1_1log_1_1Thread__local__string__appender.html#a4656e713b9ac1c6cdad3adde18de70ec">Source_obj_to_appender_map</a> = boost::unordered_map&lt;<a class="code hl_typedef" href="classflow_1_1util_1_1Unique__id__holder.html#af9cbe2432658aac398498e0a7e96405f">util::Unique_id_holder::id_t</a>,</div>
<div class="line"><a id="l00277" name="l00277"></a><span class="lineno">  277</span>                                                          boost::movelib::unique_ptr&lt;Thread_local_string_appender&gt;&gt;;</div>
<div class="line"><a id="l00278" name="l00278"></a><span class="lineno">  278</span> </div>
<div class="line"><a id="l00279" name="l00279"></a><span class="lineno">  279</span>  <span class="comment">// Constructors/destructor.</span></div>
<div class="line"><a id="l00280" name="l00280"></a><span class="lineno">  280</span><span class="comment"></span> </div>
<div class="line"><a id="l00281" name="l00281"></a><span class="lineno">  281</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00282" name="l00282"></a><span class="lineno">  282</span><span class="comment">   * Initializes object with an empty string and the streams machinery available to write to that string.</span></div>
<div class="line"><a id="l00283" name="l00283"></a><span class="lineno">  283</span><span class="comment">   * Note this is not publicly accessible.</span></div>
<div class="line"><a id="l00284" name="l00284"></a><span class="lineno">  284</span><span class="comment">   */</span></div>
<div class="line"><a id="l00285" name="l00285"></a><span class="lineno">  285</span>  <span class="keyword">explicit</span> <a class="code hl_function" href="classflow_1_1log_1_1Thread__local__string__appender.html#ad6eb4b32757f9df9823a3ee9073fa9b7">Thread_local_string_appender</a>();</div>
<div class="line"><a id="l00286" name="l00286"></a><span class="lineno">  286</span> </div>
<div class="line"><a id="l00287" name="l00287"></a><span class="lineno">  287</span>  <span class="comment">// Data.</span></div>
<div class="line"><a id="l00288" name="l00288"></a><span class="lineno">  288</span><span class="comment"></span> </div>
<div class="line"><a id="l00289" name="l00289"></a><span class="lineno">  289</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00290" name="l00290"></a><span class="lineno">  290</span><span class="comment">   * Thread-local storage for each thread&#39;s map storing objects of this class (lazily set to non-null on 1st access).</span></div>
<div class="line"><a id="l00291" name="l00291"></a><span class="lineno">  291</span><span class="comment">   * Recall `delete s_this_thread_appender_ptrs.get();` is executed at each thread&#39;s exit; so if that is non-null</span></div>
<div class="line"><a id="l00292" name="l00292"></a><span class="lineno">  292</span><span class="comment">   * for a given thread, this map is freed at that time.  Since smart pointers to Thread_local_string_appender</span></div>
<div class="line"><a id="l00293" name="l00293"></a><span class="lineno">  293</span><span class="comment">   * are stored in the map, the Thread_local_string_appender objects thus stored are also freed at that time.</span></div>
<div class="line"><a id="l00294" name="l00294"></a><span class="lineno">  294</span><span class="comment">   */</span></div>
<div class="line"><a id="l00295" name="l00295"></a><span class="lineno"><a class="line" href="classflow_1_1log_1_1Thread__local__string__appender.html#a34ac1baa61cd0c865d844a7ab622b7ea">  295</a></span>  <span class="keyword">static</span> boost::thread_specific_ptr&lt;Source_obj_to_appender_map&gt; <a class="code hl_variable" href="classflow_1_1log_1_1Thread__local__string__appender.html#a34ac1baa61cd0c865d844a7ab622b7ea">s_this_thread_appender_ptrs</a>;</div>
<div class="line"><a id="l00296" name="l00296"></a><span class="lineno">  296</span><span class="comment"></span> </div>
<div class="line"><a id="l00297" name="l00297"></a><span class="lineno">  297</span><span class="comment">  /// The target string wrapped by an `ostream`.  Emptied at construction and in fresh_appender_ostream() *only*.</span></div>
<div class="line"><a id="l00298" name="l00298"></a><span class="lineno"><a class="line" href="classflow_1_1log_1_1Thread__local__string__appender.html#a7bb2cd7d173ddc0ca3075d0475015f96">  298</a></span><span class="comment"></span>  <a class="code hl_class" href="classflow_1_1util_1_1String__ostream.html">util::String_ostream</a> <a class="code hl_variable" href="classflow_1_1log_1_1Thread__local__string__appender.html#a7bb2cd7d173ddc0ca3075d0475015f96">m_target_appender_ostream</a>;</div>
<div class="line"><a id="l00299" name="l00299"></a><span class="lineno">  299</span><span class="comment"></span> </div>
<div class="line"><a id="l00300" name="l00300"></a><span class="lineno">  300</span><span class="comment">  /**</span></div>
<div class="line"><a id="l00301" name="l00301"></a><span class="lineno">  301</span><span class="comment">   * Stores the `ostream` formatter state from construction time or time of last</span></div>
<div class="line"><a id="l00302" name="l00302"></a><span class="lineno">  302</span><span class="comment">   * save_formatting_state_and_restore_prev(), whichever occurred later; clearing (including as part of reassigning)</span></div>
<div class="line"><a id="l00303" name="l00303"></a><span class="lineno">  303</span><span class="comment">   * this pointer will invoke the destructor `~ios_all_saver()`, restoring that state to #m_target_appender_ostream.</span></div>
<div class="line"><a id="l00304" name="l00304"></a><span class="lineno">  304</span><span class="comment">   *</span></div>
<div class="line"><a id="l00305" name="l00305"></a><span class="lineno">  305</span><span class="comment">   * A pointer is used in order to be able to re-construct this at will: `ios_all_saver` does not have a &quot;re-do</span></div>
<div class="line"><a id="l00306" name="l00306"></a><span class="lineno">  306</span><span class="comment">   * construction on existing object&quot; API (not that I&#39;m saying it should... less state is good, all else being equal...</span></div>
<div class="line"><a id="l00307" name="l00307"></a><span class="lineno">  307</span><span class="comment">   * but I digress).</span></div>
<div class="line"><a id="l00308" name="l00308"></a><span class="lineno">  308</span><span class="comment">   *</span></div>
<div class="line"><a id="l00309" name="l00309"></a><span class="lineno">  309</span><span class="comment">   * @see save_formatting_state_and_restore_prev() for explanation of the feature enabled by this member.</span></div>
<div class="line"><a id="l00310" name="l00310"></a><span class="lineno">  310</span><span class="comment">   */</span></div>
<div class="line"><a id="l00311" name="l00311"></a><span class="lineno"><a class="line" href="classflow_1_1log_1_1Thread__local__string__appender.html#aebc7ceab35e8201f0c60b59a0cc93ca3">  311</a></span>  boost::movelib::unique_ptr&lt;boost::io::ios_all_saver&gt; <a class="code hl_variable" href="classflow_1_1log_1_1Thread__local__string__appender.html#aebc7ceab35e8201f0c60b59a0cc93ca3">m_target_appender_ostream_prev_os_state</a>;</div>
<div class="line"><a id="l00312" name="l00312"></a><span class="lineno">  312</span>}; <span class="comment">// class Thread_local_string_appender</span></div>
<div class="line"><a id="l00313" name="l00313"></a><span class="lineno">  313</span> </div>
<div class="line"><a id="l00314" name="l00314"></a><span class="lineno">  314</span>} <span class="comment">// namespace flow::log</span></div>
<div class="ttc" id="aclassflow_1_1log_1_1Thread__local__string__appender_html"><div class="ttname"><a href="classflow_1_1log_1_1Thread__local__string__appender.html">flow::log::Thread_local_string_appender</a></div><div class="ttdoc">Internal flow::log class that facilitates a more efficient way to get util::ostream_op_to_string() be...</div><div class="ttdef"><b>Definition:</b> <a href="thread__lcl__str__appender_8hpp_source.html#l00149">thread_lcl_str_appender.hpp:151</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Thread__local__string__appender_html_a2ac7b443898adf1696d0f24f87481520"><div class="ttname"><a href="classflow_1_1log_1_1Thread__local__string__appender.html#a2ac7b443898adf1696d0f24f87481520">flow::log::Thread_local_string_appender::save_formatting_state_and_restore_prev</a></div><div class="ttdeci">void save_formatting_state_and_restore_prev()</div><div class="ttdoc">Saves the formatting state of the ostream returned by appender_ostream() and sets that same ostream t...</div><div class="ttdef"><b>Definition:</b> <a href="thread__lcl__str__appender_8cpp_source.html#l00113">thread_lcl_str_appender.cpp:113</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Thread__local__string__appender_html_a34ac1baa61cd0c865d844a7ab622b7ea"><div class="ttname"><a href="classflow_1_1log_1_1Thread__local__string__appender.html#a34ac1baa61cd0c865d844a7ab622b7ea">flow::log::Thread_local_string_appender::s_this_thread_appender_ptrs</a></div><div class="ttdeci">static boost::thread_specific_ptr&lt; Source_obj_to_appender_map &gt; s_this_thread_appender_ptrs</div><div class="ttdoc">Thread-local storage for each thread's map storing objects of this class (lazily set to non-null on 1...</div><div class="ttdef"><b>Definition:</b> <a href="thread__lcl__str__appender_8hpp_source.html#l00295">thread_lcl_str_appender.hpp:295</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Thread__local__string__appender_html_a3f1a93d0c468efeafd83fb10e104905f"><div class="ttname"><a href="classflow_1_1log_1_1Thread__local__string__appender.html#a3f1a93d0c468efeafd83fb10e104905f">flow::log::Thread_local_string_appender::target_contents</a></div><div class="ttdeci">const std::string &amp; target_contents() const</div><div class="ttdoc">Read-only accessor for the contents of the string, as written to it since the last fresh_appender_ost...</div><div class="ttdef"><b>Definition:</b> <a href="thread__lcl__str__appender_8cpp_source.html#l00129">thread_lcl_str_appender.cpp:129</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Thread__local__string__appender_html_a4656e713b9ac1c6cdad3adde18de70ec"><div class="ttname"><a href="classflow_1_1log_1_1Thread__local__string__appender.html#a4656e713b9ac1c6cdad3adde18de70ec">flow::log::Thread_local_string_appender::Source_obj_to_appender_map</a></div><div class="ttdeci">boost::unordered_map&lt; util::Unique_id_holder::id_t, boost::movelib::unique_ptr&lt; Thread_local_string_appender &gt; &gt; Source_obj_to_appender_map</div><div class="ttdoc">Short-hand for map of a given thread's appender objects indexed by the IDs of their respective source...</div><div class="ttdef"><b>Definition:</b> <a href="thread__lcl__str__appender_8hpp_source.html#l00276">thread_lcl_str_appender.hpp:277</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Thread__local__string__appender_html_a4c67bd1c2f1ccc58288df86abda02d88"><div class="ttname"><a href="classflow_1_1log_1_1Thread__local__string__appender.html#a4c67bd1c2f1ccc58288df86abda02d88">flow::log::Thread_local_string_appender::get_this_thread_string_appender</a></div><div class="ttdeci">static Thread_local_string_appender * get_this_thread_string_appender(const util::Unique_id_holder &amp;source_obj_id)</div><div class="ttdoc">Returns a pointer to the exactly one Thread_local_string_appender object that is accessible from the ...</div><div class="ttdef"><b>Definition:</b> <a href="thread__lcl__str__appender_8cpp_source.html#l00033">thread_lcl_str_appender.cpp:33</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Thread__local__string__appender_html_a64383811f529af676dde0028f61831f7"><div class="ttname"><a href="classflow_1_1log_1_1Thread__local__string__appender.html#a64383811f529af676dde0028f61831f7">flow::log::Thread_local_string_appender::appender_ostream</a></div><div class="ttdeci">std::ostream * appender_ostream()</div><div class="ttdoc">Same as fresh_appender_ostream() but does not clear the result string, enabling piecemeal writing to ...</div><div class="ttdef"><b>Definition:</b> <a href="thread__lcl__str__appender_8cpp_source.html#l00107">thread_lcl_str_appender.cpp:107</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Thread__local__string__appender_html_a7bb2cd7d173ddc0ca3075d0475015f96"><div class="ttname"><a href="classflow_1_1log_1_1Thread__local__string__appender.html#a7bb2cd7d173ddc0ca3075d0475015f96">flow::log::Thread_local_string_appender::m_target_appender_ostream</a></div><div class="ttdeci">util::String_ostream m_target_appender_ostream</div><div class="ttdoc">The target string wrapped by an ostream. Emptied at construction and in fresh_appender_ostream() only...</div><div class="ttdef"><b>Definition:</b> <a href="thread__lcl__str__appender_8hpp_source.html#l00298">thread_lcl_str_appender.hpp:298</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Thread__local__string__appender_html_ad6eb4b32757f9df9823a3ee9073fa9b7"><div class="ttname"><a href="classflow_1_1log_1_1Thread__local__string__appender.html#ad6eb4b32757f9df9823a3ee9073fa9b7">flow::log::Thread_local_string_appender::Thread_local_string_appender</a></div><div class="ttdeci">Thread_local_string_appender()</div><div class="ttdoc">Initializes object with an empty string and the streams machinery available to write to that string.</div><div class="ttdef"><b>Definition:</b> <a href="thread__lcl__str__appender_8cpp_source.html#l00094">thread_lcl_str_appender.cpp:94</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Thread__local__string__appender_html_aebc7ceab35e8201f0c60b59a0cc93ca3"><div class="ttname"><a href="classflow_1_1log_1_1Thread__local__string__appender.html#aebc7ceab35e8201f0c60b59a0cc93ca3">flow::log::Thread_local_string_appender::m_target_appender_ostream_prev_os_state</a></div><div class="ttdeci">boost::movelib::unique_ptr&lt; boost::io::ios_all_saver &gt; m_target_appender_ostream_prev_os_state</div><div class="ttdoc">Stores the ostream formatter state from construction time or time of last save_formatting_state_and_r...</div><div class="ttdef"><b>Definition:</b> <a href="thread__lcl__str__appender_8hpp_source.html#l00311">thread_lcl_str_appender.hpp:311</a></div></div>
<div class="ttc" id="aclassflow_1_1log_1_1Thread__local__string__appender_html_af8808ca3accc5384a627bb806de4e4b1"><div class="ttname"><a href="classflow_1_1log_1_1Thread__local__string__appender.html#af8808ca3accc5384a627bb806de4e4b1">flow::log::Thread_local_string_appender::fresh_appender_ostream</a></div><div class="ttdeci">std::ostream * fresh_appender_ostream()</div><div class="ttdoc">Clears the internally stored string (accessible for reading via target_contents()),...</div><div class="ttdef"><b>Definition:</b> <a href="thread__lcl__str__appender_8cpp_source.html#l00101">thread_lcl_str_appender.cpp:101</a></div></div>
<div class="ttc" id="aclassflow_1_1util_1_1String__ostream_html"><div class="ttname"><a href="classflow_1_1util_1_1String__ostream.html">flow::util::String_ostream</a></div><div class="ttdoc">Similar to ostringstream but allows fast read-only access directly into the std::string being written...</div><div class="ttdef"><b>Definition:</b> <a href="string__ostream_8hpp_source.html#l00045">string_ostream.hpp:47</a></div></div>
<div class="ttc" id="aclassflow_1_1util_1_1Unique__id__holder_html"><div class="ttname"><a href="classflow_1_1util_1_1Unique__id__holder.html">flow::util::Unique_id_holder</a></div><div class="ttdoc">Each object of this class stores (at construction) and returns (on demand) a numeric ID unique from a...</div><div class="ttdef"><b>Definition:</b> <a href="uniq__id__holder_8hpp_source.html#l00106">uniq_id_holder.hpp:107</a></div></div>
<div class="ttc" id="aclassflow_1_1util_1_1Unique__id__holder_html_af9cbe2432658aac398498e0a7e96405f"><div class="ttname"><a href="classflow_1_1util_1_1Unique__id__holder.html#af9cbe2432658aac398498e0a7e96405f">flow::util::Unique_id_holder::id_t</a></div><div class="ttdeci">uint64_t id_t</div><div class="ttdoc">Raw integer type to uniquely identify a thing. 64-bit width should make overflow extremely hard to re...</div><div class="ttdef"><b>Definition:</b> <a href="uniq__id__holder_8hpp_source.html#l00112">uniq_id_holder.hpp:112</a></div></div>
<div class="ttc" id="adetail_2log__fwd_8hpp_html"><div class="ttname"><a href="detail_2log__fwd_8hpp.html">log_fwd.hpp</a></div></div>
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<div class="ttc" id="astring__ostream_8hpp_html"><div class="ttname"><a href="string__ostream_8hpp.html">string_ostream.hpp</a></div></div>
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